Soil Organic Carbon Dynamics and Carbon Management Index under Forest and Agricultural Land-Use Systems in the Western Himalayas

Abstract

Himalayan soils are highly susceptible to the impacts of climate change and land-use shifts. Soil organic carbon (SOC) and the carbon management index (CMI) are key measures of soil health in response to land use changes. This study assessed total organic carbon (TOC), carbon fractions, carbon pool index (CPI), CMI, and physicochemical properties in forest and agricultural land-use systems in the temperate western Himalayas. Soil samples were collected across 32 distinct sites representing forest (FS), wheat (WS), rice (RS), and maize (MS) systems (n = 32). FS exhibited the highest average TOC (25.6 g kg-1), followed by MS (19.3 g kg-1), WS (15.2 g kg-1), and RS (14 g kg-1). TOC levels differed significantly between land-use categories (ANOVA; F = 13.4, P< 0.001), with all agricultural systems showing significantly lower TOC levels than forests. The maximum concentration of labile carbon (LC) was identified in FS (4.3%), while the lowest was observed in WS (2.8%). MS had the highest CPI (0.75), whereas RS had the highest average CMI (85.5), indicating distinct carbon management dynamics despite lower baseline TOC. TOC was positively correlated with altitude and electrical conductivity but negatively correlated with soil pH. Multiple linear regression (R2 = 0.70) confirmed land-use type as the primary predictor of TOC variation, showing significant reductions for RS (11.6 g kg-1), WS (10.7 g kg-1), and MS (4.9 g kg-1) compared to the forest baseline (P< 0.05). Principal component analysis successfully differentiated agricultural and forest systems based on topography, soil properties, and carbon pools. The primary cause of SOC depletion is the initial conversion of forests to farmland, underscoring the need for climate smart land management to maintain ecosystem services and replenish regional carbon stocks.